1. Field of the Invention
The present invention relates to a metal oxide-containing kenyaite catalyst, a method for preparing the same, and a method for preparing ε-caprolactam from cyclohexanone oxime by applying the catalyst to gas phase Beckmann rearrangement of cyclohexanone oxime.
2. Description of the Background Art
A process for preparing ε-caprolactam from cyclohexanone oxime is one of the industrially important processes. ε-Caprolactam is a raw material for preparing nylon-6. A general commercial production process for preparing ε-caprolactam is carried out by the Beckmann rearrangement of cyclohexanone oxime in a liquid phase by using a sulfuric acid as a catalyst.
However, several problems are caused from using the sulfuric acid as a catalyst in the process for preparing ε-caprolactam. For example, after the Beckmann rearrangement, a large amount of ammonia must be used as a neutralizer for removing the sulfuric acid used as the catalyst, and thereby ammonium sulfate, which is economically disadvantageous, is produced as by-products in the amount of 2 to 3 tons per a ton of ε-caprolactam. Since a great cost is incurred in collecting and processing the by-product, the production of such by-product makes the unit cost of production of ε-caprolactam increased. In addition, since sulfuric acid used as a catalyst is a very strong acid, several problems are generated. For example, sulfuric acid makes a reaction vessel corroded and is difficult to be handled, to cause many problems in safety and environment.
In order to solve the foregoing problems of the conventional process for preparing ε-caprolactam by using sulfuric acid as the catalyst, a process for performing Beckmann rearrangement of cyclohexanone oxime in a gas phase by replacing sulfuric acid with a solid acid has been developed and actively investigated. For example, silica-alumina, solid phosphoric acid, boric acid, a metal oxide and zeolite have been suggested as the solid acid catalysts for the gas phase Beckmann rearrangement of cyclohexanone oxime.
Nevertheless, the researches on the solid acid catalysts do not show satisfactory results in the lifetime of catalysts, the conversion of cyclohexanone oxime and the selectivity of ε-caprolactam. Therefore, It is necessary to develop a solid acid catalyst having excellent catalytic performance in the gas phase Beckmann rearrangement of cyclohexanone oxime.
In order to develop the solid acid catalyst having excellent catalytic performance in the gas phase Beckmann rearrangement of cyclohexanone oxime, the Beckmann rearrangement using various kinds of zeolite catalysts different in pore size and shape has been attempted. In addition, so as to improve performance of the zeolite catalyst, there have been suggested various methods, for example, controlling acid strength and concentration by changing Si/Al mol ratio, substituting with a different metal in the framework of zeolite, controlling a particle size and an external surface area of zeolite, and modifying a catalyst active site by treating zeolite with an acid or base. However, such methods have not obtained advantageous results in conversion of cyclohexanone oxime, yield of ε-caprolactam and catalytic durability.
On the other hand, in accordance with various research results on the solid acid catalysts in the gas phase Beckmann rearrangement of cyclohexanone oxime, in order to obtain excellent catalytic performance in the gas phase Beckmann rearrangement of cyclohexanone oxime, it is advantageous that the solid acid catalyst has a relatively weak acid site or a medium acid site. When the solid acid catalyst has a strong acid site, side reactions increase (Catalysis Letter, vol 78, p. 189, 2002).
The present inventors have made researches to develop a sold acid catalyst for the gas phase Beckmann rearrangement of cyclohexanone oxime, and finally found out the fact that the conversion of cyclohexanone oxime and the yield of ε-caprolactam could be improved in the gas phase Beckmann rearrangement of cyclohexanone oxime using a solid acid catalyst being prepared by introducing a metal oxide to a layered silicate having a kenyaite structure synthesized in the presence of an amine template and has a weak or medium acid site, to complete the present invention.